1. Field of the Invention
The present invention relates to a system and a method for delivery of a vapor phase product to a point of use. The present invention also relates to an on-site chemical distribution system and to a method for on-site distribution of a chemical. The invention has particular applicability in the delivery of electronic specialty gases used in the manufacture of semiconductor devices to one or more semiconductor processing tools.
2. Description of the Related Art
In the semiconductor manufacturing industry, different chemicals are supplied to processing tools in gaseous form for carrying out a variety of semiconductor fabrication processes. Examples of such processes include diffusion, chemical vapor deposition (CVD), etching, sputtering and ion implantation. These chemicals are conventionally referred to as electronic specialty gases (ESG's).
Many of the chemicals employed in the above processes, while introduced to the processing tools in the gaseous state, are stored as liquids under their own respective vapor pressures. Typically, the liquid chemicals have room temperature vapor pressures greater than atmospheric pressure.
These chemicals are conventionally stored in gas cylinders which are housed within gas cabinets. A typical volume of such a gas cylinder is less than about 50 liters. A partial list of chemicals stored in this manner, the pressures under which they are stored and their critical pressures are provided below in Table 1:
TABLE 1 ______________________________________ Vapor Pressure CriticalGas at Pressuregree. C. Chemical Formula (psia)) ______________________________________ Ammonia NH.sub.3 129 1636 Boron Trichloride BCl.sub.3 1071 Carbon Dioxide CO.sub.2 1118 Chlorine 634.7 Chlorotrifluoride ClF.sub.3 837.4 Dichlorosilane SiH.sub.2 Cl.sub.2 24 746.6 Disilane 48i.sub.2 H.sub.6 956.9 Hydrogen Bromide HBr 1240 Hydrogen Chloride HCl 1198 Hydrogen Fluoride HF 940.2 Nitrous Oxide N.sub.2 O 760 1050 Perfluoropropane C.sub.3 F.sub.8 115 388.5 Sulfur 545.0 Hexafluoride Tungsten 619.1 Hexafluoride ______________________________________
A single gas cabinet typically supplies the chemical vapor to a single or at most several semiconductor processing tools. Operation of the gas cabinets and the cylinders housed therein can be a hazardous, labor intensive and costly activity. As the chemical is depleted, it is imperative that the gas cylinder be replaced with careful and proper handling procedures.
In order to reduce the total number of gas cabinets required in the semiconductor manufacturing facility, it has recently been proposed that a single gas cabinet service multiple processing tools. Since the volumes of the cylinders housed in the gas cabinets do not increase with the number of processing tools being serviced, replacement frequency of the cylinders in the cabinets necessarily increases. It is, however, desirable to minimize the frequency of cylinder replacement, not only for safety concerns but also to reduce the risk of introducing impurities that may cause significant product loss.
In addition to increasing the frequency of gas cylinder replacement, the instantaneous flowrate of the gas being withdrawn from each cylinder increases with the additional processing tools serviced by a given gas cabinet. Such an increase in flowrate can lead to the presence of entrained liquid droplets in the gas stream, which can result in flowrate fluctuations, accelerated corrosion and premature failure of flow control components in the gas distribution system. Furthermore, the corrosion products can lead to contamination of the highly pure process gases. This contamination can have deleterious effects on the processes being run, and ultimately on the manufactured semiconductor devices.
To meet the requirements of the semiconductor processing industry and to overcome the disadvantages of the related art, it is an object of the present invention to provide novel systems for delivery of a chemical stored as a liquid under its own vapor pressure. The systems make possible the simultaneous servicing of multiple processing tools and additionally can perform a purification function, whereby highly pure gases useful in semiconductor manufacture can be produced. Because of such purification function, the systems make possible the use of a relatively low purity starting material, which material would otherwise not be useful, for example, in semiconductor manufacturing.
According to one aspect of the invention, entrained liquid droplets in the gas obtained from the liquid chemical can be minimized or eliminated. As a result, single phase process gas flow can be obtained, in contrast to known systems and methods.
It is a further object of the present invention to provide novel methods for delivery of a chemical stored as a liquid under its own vapor pressure, which methods can be practiced on the inventive systems.
It is a further object of the present invention to provide a novel on-site chemical distribution system, and a method for on-site chemical distribution which method can be practiced on the system.
Other objects and aspects of the present invention will become apparent to one of ordinary skill in the art upon review of the specification, drawings and claims appended hereto.